1. Field of the Invention
The present invention relates to a process for preparing subdenier fibers from isotropic polymer solutions which may be collected in the form of pulp-like short fibers, fibrids, rovings, and mats. The invention also contemplates and includes products having novel subdenier fiber structures which are produced according to the aforementioned process.
2. Description of the Prior Art
Different methods are known in the art for preparing sheet structures and non-woven articles of discontinuous thermoplastic fibers.
For example, Butin et al., U.S. Pat. No. 3,849,241, and European Publication 0166830, disclose directing gas streams at a fiber-forming polymer in the molten state and then collecting the fibers on a screen.
It is also known in the art to flash extrude a continuous fibrillated polymeric structure and to shred it by directing a stream of fluid against the structure at the moment of its formation. (See, Raganato et al., U.S. Pat. No. 4,189,455).
However, none of the foregoing references disclose a jet-attenuating process for preparing subdenier fibers from isotropic solutions.
Morgan, U.S. Pat. No. 2,999,788 describes the preparation of fibrids of various synthetic organic polymers and their use in making synthetic sheet structures, such as papers. Such papers, when prepared from poly(meta-phenylene isophthalamide) fibrids, are useful in electrical applications, especially when combined with poly(meta-phenylene isophthalamide) short fibers (floc). As disclosed by Gross, U.S. Pat. No. 3,756,908, the poly(meta-phenylene isophthalamide) fibrids of the art are filmy particles which act as a binder for the floc and impart good electrical properties. However, these fibrids have a deficiency in that they seal the papers excessively and so act to reduce porosity. Porosity is a valuable property because it facilitates coating and saturation of the papers with varnishes and resins, a method well known in the art to modify and improve properties of electrical papers.
An object of the present invention is to prepare new pulp-like poly(meta-phenylene isophthalamide) fibrids. These pulp-like fibrids may be used to prepare sheet structures, such as papers which demonstrate improved porosity and electrical properties. These sheet structures may be used in preparing laminate and composite structures.